The present invention relates to a device for the fermentation of drinks containing sugar and in particular the preparation of sparkling wine such as champagne by a second fermentation, or refermentation of a still wine in the bottle.
The traditional so-called "champagne" method consists of adding a "liqueur de tirage" containing sugar and the fermentation yeast necessary for the conversion of the sugar into carbon dioxide to still ordinary wine, which has already undergone a first alcohol fermentation. Bottling may be carried out before or after these additional stages.
The bottles are then corked using a hollow plastic stopper inserted into the neck of the bottle and sealed by crimping a metal cap. They are then generally stored horizontally "on slats" for a long period of time lasting from several months to several years in cedars where the temperature is kept constant, generally between 10 and 15.degree. C. so that fermentation takes place with a corresponding rise in pressure or "bottle fermentation" in the bottles.
At the end of this long fermentation period, each bottle must be shaken individually several times in order to dislodge the fermentation deposit which might stick to the walls of the bottle. During this shaking period the bottles are also inclined then stored "on the point", that is to say inclined with the neck downwards, to facilitate the decanting of the yeasts and encourage the fermentation waste products to be deposited inside the hollow plastic stopper situated in the neck of the bottle.
Once shaking is completed, the bottles are transported vertically, with the neck downwards, and are plunged in a refrigeration brine bath maintained at about -20.degree. C. in order to form, by freezing, a plug of frozen wine containing the fermentation yeast waste products.
The bottles then undergo a disgorging operation which consists of vertically placing the bottles with the thus frozen neck upwards and of decapping them, which causes, under the action of the pressure inside the bottle, the ejection of the plastic stopper together with the frozen plug containing the fermentation sediments.
The original level of the bottles is then restored by the addition of a "liqueur d'expedition" and the bottle is sealed with a permanent stopper which is generally made of cork.
The traditional so-called "champagne" method that has just been described requires a large workforce, in particular after fermentation when the bottles are shaken, an act often carried out by hand. This method involves a large surface area for storing the bottles on special racks and a rather long storage time which may be more than one month. In addition, the traditional method includes a stage of freezing the neck of the bottles, which is indispensable for the elimination of the yeasts.
Attempts have been made to try to remedy these drawbacks.
U.S. Pat. No. 4,792,454 assigned to Millipore Corporation, the parent company of the assignee of this application, describes a process for fermenting wine in the bottle according to the champagne method. This prior art process includes the introduction of a tubular filter cartridge into the neck of the bottle of wine which has had added to it the quantity of sugar necessary to obtain the desired final pressure of carbon dioxide. This cartridge has a perforated tubular body, externally coated with a hydrophilic filter membrane and a hydrophobic filter membrane and contains the yeasts necessary for the fermentation of wines containing sugar with release of carbon dioxide. The use of such a filter cartridge has the advantage of eliminating the need for a shaking stage which allowed the deposit of yeasts to be concentrated in the neck of the bottle, as well as the requirement of freezing the neck of the bottle, which allowed the plug containing the yeast residues to be frozen and ejected, since the yeasts are no longer in contact with the inside of the bottle. The technique described in this U.S. patent does, however, have certain drawbacks.
In fact, it has been observed that the rise in pressure of the carbon dioxide in wine bottles fitted with a cartridge according to the teachings of U.S. Pat. No. 4,792,454 required a longer time than that necessary for fermentation according to the traditional champagne method. Such an increase in the duration of bottle fermentation results in an unacceptable modification of the organoleptic properties of the wine which has undergone a second fermentation under these conditions.
Furthermore, during experiments carried out to identify the mechanisms involved during bottle fermentation according to the aforementioned U.S. patent, it was noted that the cartridge, filled with yeast and immersed in wine, quickly emptied itself of any liquid under the pressure of the carbon dioxide produced by the yeast. The gas thus accumulated inside the cartridge only escaped (in the form of bubbles) through the vent, constituted by the hydrophobic membrane, when the pressure was sufficient to overcome the forces of surface tension. This prior art filter cartridge therefore acts as a surface fermentor, in which only the yeasts in contact with the hydrophilic membrane are wetted by the wine and can therefore live and consume the sugar.
Furthermore, during the fermentation reaction, the yeasts which consume the sugar while producing mainly ethanol and carbon dioxide release energy in the form of heat. Hence the wine in contact with the yeasts is depleted of sugar and simultaneously its temperature is raised slightly by the fermentation reaction, and then it is replaced due to thermal convection by wine which is colder and richer in sugar.
In addition, the structure itself of the cartridge described in the U.S. patent mentioned above, where the surface of the membrane lined on the inside with yeasts acts as a heat generator, limits the convection currents due to its cylindrical shape and its bulkiness in the neck of the bottle.